Emissions from a Stirling engine-powered 1986 model light-duty truck were measured using current EPA (chassis dynamometer) emissions certification procedures and certain specialized tests. Three fuels were used including unleaded gasoline, a blend of MTBE in unleaded gasoline, and JP-4. City (FTP) cycles and Highway (FET) cycles were run on all three fuels, and emissions measured during the cycles included hydrocarbons (HC), carbon monoxide (CO), and oxides of nitrogen (NOx). Fuel economy was also calculated for these tests. Additional pollutants measured during some of the tests included aldehydes, 1,3-butadiene, individual hydrocarbon species, and total particulate matter.
In addition to the cyclic schedules, steady-state conditions were run on JP-4 and straight gasoline for regulated emissions and fuel economy. The conditions consisted of several simulated gradients at three vehicle speeds, plus idle. During the evaluations on the MTBE blend and some of those on gasoline, engine parameters such as air/fuel ratio and exhaust gas recirculation (EGR) rate were changed from test to test in order to evaluate their effects.
It was found in general that the Stirling engine was capable of low regulated emission levels on all the test fuels utilized, without a catalytic converter. Fuel economy of the vehicle was in the same range as a similar vehicle with a gasoline internal combustion engine, and performance was adequate to drive the required cycles without difficulty. Both EGR rate and A/F ratio had substantial effects on emissions, as expected. Cold-start emissions (those within a few minutes after startup) constituted most of the regulated pollutants emitted when the engine was adjusted optimally on each fuel.